Lord Toranaga is a sick man. Sick in his heart, grieving the loss of his son Nagakado, who died in a vain fight on his father’s behalf. Sick in his body, having contracted an illness on the long road back to Edo for Nagakado’s burial. The central scene of this week’s “Shogun” — perhaps the scene from the series so far — confronts vassal and viewer alike with an even more troubling question, one that it draws out for minute after excruciating minute: Is Lord Toranaga sick in his mind as well? Toranaga gathers his vassals in Edo to certify his big decision. He will not authorize Crimson Sky, the plan to attack Osaka and overthrow Lord Ishido and the Council of Regents. Once the customary mourning period is over, he will dutifully march off to his execution, and many of them must join him in marching to theirs. He wants their signatures to this effect.